If it is a six pin it has two common cathodes and if it is an eight pin it has four cathodes in a quad photodiode. Just use one Anode (Pin 1) and the Cathode Common (Pin 2) on most. You can determine the anode from the cathode with a multimeter. Joe
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It has 10 pins and can you be specific by what you mean by testing it with multimeter
10 pins how nice. You will have ether NCs (No Contact) or multiple Common Cathodes. If you don’t have a part number give up on finding a data sheet. Remember on your multimeter black probe Cathode and red probe Anode. A photo diode is a diode so set your multimeter for continuity, then put the black probe on one pin and touch the rest of the pins one at a time with the red probe. Make sure there is no light on the photo diode. If you get a reading between the two pins that is forward bias, the current flow is from red probe to the black probe. If you get a reading from all the pins the pin the black probe is on is a Common Cathode. If you don’t get a reading after checking all the pins, put the red probe on the pin you had the black probe on and check all the pins again with the black probe. If you still don’t get a reading that pin is NC. If you get readings on two or more pins the black probe is a Common Cathode. With a photo diode connect it reverse bias and expose it to the right light frequency and you will get a current flow in the reverse direction. See my Instructable Photo Components & Testing.https://www.instructables.com/id/Photo-Components-Testing/ Joe
Find a datasheet ?